An important task of a satellite operator is to ensure that the Radio Frequency (RF) signals transmitted by earth-bound satellite antennas do not interfere with each other as they are received at the satellite. Normally, resulting Radio Frequency Interference (RFI) at the satellite is easily detectable because, in a traditional “bent pipe” configuration, all transmissions to the satellite are shifted in frequency and, for all practical purposes, immediately transmitted back to the ground. The received RF emissions can then be analyzed using, e.g., a ground based spectrum analyzer and any interference can be uncovered.
With the advent of satellite architectures employing on-board processing, where the uplink transmissions are terminated at the satellite, uplink RFI cannot be seen on the ground. That is, in an on-board processing system, the uplink signal is demodulated on the satellite, and converted into digital data using a modem complex. The modem complex passes the data to a computer system or processor that operates on the data and then passes new downlink data back to the modem complex. The modem complex then synthesizes and modulates the downlink data for downlink transmission. Thus, the nature of any RFI present in a signal received at the satellite is lost by the time the modem complex has finished its receive processing. This makes detection of RFI nearly impossible and can result in undetected poor received signal quality at the satellite.